Continued Shelf-life Testing of Rigid Spray Foams with Systems Based on Methyl Formate

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1 ABSTRACT TITLE: Continued Shelf-life Testing of Rigid Spray Foams with Systems Based on Methyl Formate Author(s): John Murphy, Foam Supplies, Inc. ABSTRACT: Reactivity drift in polyurethane spray foams has always been a concern since the use of CFC-11. A slower reactivity in spray foams can be attributed to a number of reasons considering the number of raw materials present in the resin blend. In this paper I will study each of the acid producing ingredients in the polyol blend to determine which ingredient(s) has the greatest effect on shelf life stability. This will be accomplished by performing a shelf life study on systems with one or more of the acid generating ingredients removed and seeing how it compares to a standard in terms of reactivity. From this testing, an optimum formulation will be developed with an optimum shelf life Rider Trail N. Earth City, MO

2 Continued Shelf-life Testing of Rigid Spray Foams with Systems Based on Methyl Formate DAVID MODRAY Foam Supplies, Inc North Rider Trail Earth City, MO ABSTRACT Reactivity drift in polyurethane spray foams has always been a concern since the use of CFC-11. A slower reactivity in spray foams can be attributed to a number of reasons considering the number of raw materials present in the resin blend. In this paper I will study each of the acid producing ingredients in the polyol blend to determine which ingredient(s) has the greatest effect on shelf life stability. This will be accomplished by performing a shelf life study on systems with one or more of the acid generating ingredients removed and seeing how it compares to a standard in terms of reactivity. From this testing, an optimum formulation will be developed with an optimum shelf life. INTRODUCTION In a previous paper[1], the optimum catalyst package for a typical spray foam blown with ecomate was selected. This catalyst package was the least affected by the acids generated by other ingredients in the resin blend. In the following experiments, the shelf life of the same spray foam will be studied in more detail. This time, minor changes will be made to the formula and the effect will be studied in a long-term shelf life study. The reactivity of each formula will be compared to others to determine what ingredient most affects the shelf life of the spray foam formula. Polyurethane spray foams derive their fast reactivity from the catalyst package. While it provides rapid reactivity, it is vulnerable to degradation from acids formed in the resin blend. Acids form in the resin blend via hydrolysis. Acids can be generated from hydrolysis of polyester polyols, certain flame retardants, certain blowing agents, and other additives. Then the acids can interact with the catalysts, both amine and metal, in the resin blend causing a loss in reactivity. This becomes evident when the spray foam takes longer to react and cure. From an application standpoint, slower reacting spray foam can cause sagging or drooping, which diminishes foam performance and generates solid foam waste. In polyurethane resin blends, there are two reactions that can create acids in the resin blend. First, there is the hydrolysis of an ester group. This is an equilibrium reaction between an ester group and water. This gives a carboxylic acid and an alcohol. This reaction is shown in Figure 1. Figure 1. Ester Hydrolysis Reaction

3 The carboxylic acid formed can then interact with the catalyst causing slower reactivity. The second hydrolysis reaction is the hydrolysis of a phosphate ester. Phosphate esters are a commonly used component in flame retardant chemicals. In this reaction, one of the legs of a phosphate group is removed, giving an alcohol, and leaving an acidic group on the phosphate. This is shown in Figure 2. Figure 2. Phosphate Ester Hydrolysis Reaction The phosphate acid can then interact with the catalysts, causing slower reactivity. While spray polyurethane foams are initially made with a very rapid reactivity, often the reactivity slows down with time leading to application problems. A polyurethane foam formulator must keep in mind the possibility of hydrolysis when adding ingredients to the polyol blend, as hydrolysis can lead to a change in reactivity profile over time. In the following experiments, several different ingredients will be tested for their effects on the shelf life of a polyurethane spray foam. EXPERIMENTAL A general purpose spray foam formulation was evaluated. The formulation is designed to be a rigid spray formulation with a nominal 2 pounds per cubic foot free rise density. The resin blend used was 12B56. The formula is shown in Table 1. Table 1. Blend 12B56 Chemical % Amine Polyol 15.0 Polyester Polyol Sucrose-Glycerin Polyol 33.0 Tris (1-Chloro 2-propyl) Phosphate (TCPP) 20.0 Silicone Surfactant 1.5 Water 2.0 Amine Blowing Catalyst B 2.0 Metal Gelling Catalyst ecomate 5.0 Several variations were made to this formula, each named according to a slight change in the base formula. Table 2 shows each formula and the variation associated with it.

4 Formula Name Normal Table 2. Formula Variation Table Variation from formula 12B56 No Change; Same as it is written above Control Polyester polyol 1 and TCPP have been replaced with Glycerin Polyol 2 TEP The 20% TCPP has been replaced with 12% TEP (Triethyl phosphate) FR1 The TCPP has been replaced with Flame Retardant 1 FR2 The TCPP has been replaced with Flame Retardant 2 FR3 The TCPP has been replaced with Flame Retardant 3 PS2 The Polyester Polyol 1 has been replaced with Polyester Polyol 2 PS3 The Polyester Polyol 1 has been replaced with Polyester Polyol 3 PS4 The Polyester Polyol 1 has been replaced with Polyester Polyol 4 365mfc The ecomate has been replaced by a molar equivalent of 365mfc PE2 The TCPP has been replaced with Glycerin Polyol 2 Enough resin blend of each formula was made for 7 tests of each formula. The resin blends were then reacted with polymeric MDI at a weight ratio of 100 parts isocyanate to 93 parts resin blend. All formulas were tested using a high-speed pneumatic hand mixer. All chemicals were at 25 o C (77 o F) when reacted. The foams were tested for cream time and tack free time. The results are given in Table 3. Table 3. Initial Test Results Formula Name Cream Time (sec.) Tack Free Time (sec.) Normal 3 11 Control 3 13 TEP 2 12 FR FR FR PS PS PS mfc 3 11 PE An accelerated aging test was started on all of these formulas. They were placed in metal cans in an oven at 50 o C (122 o F). This is a standard aging temperature used in the industry for shelf life stability testing. Our own test data shows that one week in 50 o C stability is equivalent to about 6-8 weeks at ambient temperature. After one week, the 11 samples were removed from the oven, brought back to 25 o C and tested once again. The results are given in Table 4.

5 Table 4. 1 Week Aged Test Results Formula Name Cream Time (sec.) Tack Free Time (sec.) Normal 4 13 Control 4 15 TEP 3 12 FR FR FR PS PS PS mfc 3 11 PE All formulas were again placed back in the oven at 50 o C (122 o F). After another two weeks of aging, the formulas were removed from the oven, brought back to 25 o C, and tested again. These results are in Table 5. Table 5. 3 Week Aged Test Results Formula Name Cream Time (sec.) Tack Free Time (sec.) Normal 4 13 Control 4 15 TEP 3 12 FR FR FR PS PS PS mfc 3 13 PE This process of aging and testing was repeated at 5 weeks aged, 7 weeks aged, and 10 weeks aged. These results are in Table 6, Table 7, and Table 8. Table 6. 5 Week Aged Test Results Formula Name Cream Time (sec.) Tack Free Time (sec.)

6 Normal 4 15 Control 4 16 TEP 4 14 FR FR FR PS PS PS mfc 3 13 PE Table 7. 7 Week Aged Test Results Formula Name Cream Time (sec.) Tack Free Time (sec.) Normal 4 17 Control 4 17 TEP 4 16 FR FR FR PS PS PS mfc 3 14 PE Table Week Aged Test Results Formula Name Cream Time (sec.) Tack Free Time (sec.) Normal 4 17 Control 4 15 TEP 4 16 FR FR FR3 4 16

7 PS PS PS mfc 4 17 PE Analyzing the data it is evident that the cream time did not shift significantly on any formula except for FR2. On the other hand, the tack free time data varied greatly from one formula to the next. This was dependent on the amount of acid produced and the effect of the acid on the catalyst package. As each formula aged, it produced a distinct reactivity curve. Each reactivity aging curve was compared to others in the same group to determine what had the greatest effect on reactivity drift. First, the formulas with different Flame Retardants will be analyzed. In Table 9, the tack free time data is organized by each formula and by weeks in stability. Table 9. Tack Free Times: Flame Retardants Formula Name Initial 1 Week 3 Weeks 5 Weeks 7 Weeks 10 Weeks Normal (TCPP) TEP FR FR FR By plotting the data from Table 9 on a graph (Figure 3), a trend for each formula can be seen oC Reactivity Stability Flame Retardant Series Tack Free Time (seconds) TCPP TEP FR1 FR2 FR Weeks in 50oC Stability Figure 3. Graph of Reactivity Drift with Different Flame Retardants

8 While each formula with flame retardant showed some slow down, some flame retardants worked better than others. On the graph in Figure 3, it is evident that FR2 performed poorly showing a large reactivity drift with time. On the other hand, TEP had the smallest drift of the flame retardants tried. TCPP, FR1, and FR3 also performed well in the study with just slightly more drift than TEP. The next group analyzed in the polyester polyol group. There were four polyester polyols tested in formula 12B56. In Table 10, the reactivity data has been organized by polyester polyol and by weeks in 50 o C stability. Table 10. Tack Free Times: Polyester Polyols Formula Name Initial 1 Week 3 Weeks 5 Weeks 7 Weeks 10 Weeks Normal (PS1) PS PS PS By plotting the data from Table 10, a trend for each formula can be seen. This data has been plotted in Figure oC Reactivity Stability Polyester Polyol Series Tack Free Time (seconds) PS1 PS2 PS3 PS Weeks in 50oC Stability Figure 4. Graph of Reactivity Drift with Different Polyester Polyols In the graphs of polyester polyols, there is no discernable difference in the reactivity drift curves. This seems to suggest that reactivity drift is unaffected by polyester choice. Two things in this formula should be noted. First, the formula only contains 21% polyester polyol in the resin portion and certain formulas will contain a much greater amount. Second, only four polyester polyols were tested in this study and there are many more that were not tested.

9 The third set to be analyzed is the blowing agents. In this study, only two were tested, ecomate and 365mfc. Both of these had their reactivity data organized in Table 11. Table 11. Tack Free Times: Blowing Agents Formula Name Initial 1 Week 3 Weeks 5 Weeks 7 Weeks 10 Weeks Normal (ecomate ) mfc When the data in Table 11 is plotted, a trend for each formula can be seen. This data has been plotted in Figure oC Reactivity Stability Blowing Agent Series Tack Free Time (seconds) ecomate 365mfc Weeks in 50oC Stability Figure 5. Graph of Reactivity Drift with Different Blowing Agents The graphs in Figure 5 seems to suggest that the ecomate blown foam has a little bit more drift than 365mfc at the beginning of the study, however both blowing agents followed a similar trend and eventually merged at the same reactivity at the end of the study. The last set evaluated examines the 12B56 formula on a more fundamental level. This set has Glycerin Polyol 2 put in place of some ingredients of the polyol blend. It is assumed that Glycerin Polyol 2 will not contribute to reactivity drift. For review, Table 12 contains the description of each formula. Table 12. Formula Variation Table Formula Name Normal Variation from formula 12B56 No Change Control Polyester polyol 1 and TCPP have been replaced with Glycerin Polyol 2

10 PE2 The TCPP has been replaced with Glycerin Polyol 2 Next, the reactivity data of these three formulas will be organized by formula and by weeks in 50 o C stability. This data is shown in Table 13. Table 13. Tack Free Times: Flame Retardants Formula Name Initial 1 Week 3 Weeks 5 Weeks 7 Weeks 10 Weeks Normal Control PE When the data is plotted, a trend for each formula can be seen. This data is plotted in Figure oC Reactivity Stability PE2 Substitution Series Tack Free Time (seconds) normal control PE Weeks in 50oC Stability Figure 6. Graph of Reactivity Drift with Glycerin Polyol 2 Substitution In this graph, the Control performed the best with only 2 seconds of drift. Then PE2 was second with 4 seconds of drift. Then Normal had 6 seconds of drift. This data suggests that both the TCPP and polyester polyol are contributing to reactivity drift. It is not conclusive as to which contributes more to drift since the difference in drift is so small. CONCLUSIONS Optimization of any polyurethane foam formulation is imperative. All properties of the foam including compression strength, nominal density, burn characteristics, etc. have to be considered. In the case of spray foam, optimizing the shelf life reactivity is of utmost importance.

11 When assembling a polyurethane spray foam, it is important to choose ingredients that will have the lowest impact on reactivity stability. Doing so will increase the shelf life of a spray foam formulation. Proper flame retardant selection was found to be the most important to spray foam shelf life. The wrong flame retardant selection can lead to a spray foam with a very short shelf life as demonstrated by formula FR2. Several flame retardants showed good stability to be used in a spray foam, but TEP showed the lowest drift in the study. Good polyester polyol selection is important to spray foam shelf life, although the study seems to indicate that the choice of polyester polyol does not influence reactivity drift. It is likely that more polyester polyol will lead to more reactivity drift, but further testing would be required to confirm this. While blowing agent choice does impact shelf life stability of spray foam, it appears that ecomate has very little effect on the system since it performed just as well as an HFC in the same formula. Fundamentally, the shelf life of a spray foam is most affected by the flame retardant and the polyester polyol since substituting for them with a glycerin polyol led to less reactivity drift. A spray foam formula optimized for reactivity drift will have TEP as the flame retardant, a well suited polyester polyol, ecomate blowing agent, and as low an amount allowable of flame retardant and polyester polyol. Using these ingredients will lead to a polyurethane spray foam with a very long (greater than eight months) shelf life. REFERENCES BIOGRAPHY 1. David L. Modray: Shelf Life Evaluation of Polyurethane Rigid Foams Blown with ecomate, CPI Proceedings 2013 David Modray David received his BS in Chemical Engineering in 1995 from the University of Missouri-Columbia. For 18 years he has been employed by FSI as a research chemist. He is currently assigned to new product development where he has developed several commercially sold rigid foam systems. For the last 14 years he has been one of the primary formulators of ecomate foam systems.

12 Continued Shelf-Life Testing of Rigid Spray Foams with Systems Based on Methyl Formate David L. Modray 5 June 2014

13 Continued Shelf-Life Testing of Rigid Spray Foams with Systems Based on Methyl Formate The Goal: To determine which ingredients will produce a polyurethane spray foam formula a shelf life > 8 months The Experiment: Test different ingredients in a spray foam formula, and Test each formula at fixed intervals in an accelerated aging test

14 Advantages of using polyurethane spray foam: Rapid reactivity profile Can be sprayed directly on the surface to be foamed The foam will stay where it is sprayed, it will not droop or sag

15 A major disadvantage of spray foam is its limited shelf life. After a short period of time acids can form via hydrolysis: Acids are generated from polyester polyols, flame retardants, blowing agents, and other additives These acids then attach themselves to the catalysts present and prevent the catalysts from working effectively This causes the spray foam to take longer to react/cure resulting in sagging/drooping

16 Hydrolysis Reactions How does acid formation occur in the polyol blend? Let s look at two of the acid generating reactions one at a time and in greater detail: First, ester hydrolysis will be examined. A ester can combine with any water present in the resin blend and generate an alcohol and a carboxylic acid: O R C O R + H 2 O R C O H O + H O R The acid produced can then interact with catalysts in the resin blend causing a slower reactivity

17 Hydrolysis Reactions Another hydrolysis reaction is the hydrolysis of a phosphate ester. Phosphate esters are commonly used in flame retardant chemicals In this hydrolysis, one of the legs of a phosphate group is removed, giving an alcohol and leaving an acidic group on the phosphate: R O O P O R + H 2 O H O O P O R + R O H O O R R The phosphate acid can then interact with the catalysts, causing a slower reactivity.

18 Experimental A general purpose spray foam formulation was evaluated. A previous experiment obtained an optimum catalyst package For this experiment, resin blend 12B56 was assembled: Chemical % Amine Polyol 15.0 Polyester Polyol Sucrose-Glycerin Polyol 33.0 Tris (1-Chloro 2-propyl) Phosphate (TCPP) 20.0 Silicone Surfactant 1.5 Water 2.0 Amine Blowing Catalyst B 2.0 Metal Gelling Catalyst ecomate 5.0

19 Experimental Then several variations were made to the base formula, each named according to a slight change made to the formula: Formula Name Normal Variation from 12B56 No Change; Same as it is on the previous slide Control Polyester Polyol 1 and TCPP have been replaced with Glycerin Polyol 2 TEP The 20% TCPP has been replaced with 12% TEP (Triethyl Phosphate) FR1 The TCPP has been replaced with Flame Retardant 1 FR2 The TCPP has been replaced with Flame Retardant 2 FR3 The TCPP has been replaced with Flame Retardant 3 PS2 The Polyester Polyol 1 has been replaced with Polyester Polyol 2 PS3 The Polyester Polyol 1 has been replaced with Polyester Polyol 3 PS4 The Polyester Polyol 1 has been replaced with Polyester Polyol 4 365mfc The ecomate has been replaced with a molar equivalent of 365mfc PE2 The TCPP has been replaced with Glycerin Polyol 2

20 Experimental All formulas were tested using the high-speed pneumatic hand mixer. All chemical temperatures were 25 o C (77 o F) when reacted. The foams were tested for cream time and tack free time. An accelerated aging test was started on all 11 of these formulas. They were placed in metal cans in an oven at 50 o C (122 o F). After one week, the 11 samples were removed from the oven, brought back to 25 o C and tested once again. Initial Test In Oven 1 Week 1 Week Test

21 Experimental All formulas were again placed back in the oven at 50 o C (122 o F). After another two weeks of aging, the formulas were removed from the oven, brought back to 25 o C, and tested again. This process of aging and testing was continued with tests run at 5 weeks, 7 weeks, and 10 weeks. In Oven Test 1 week aged 3 weeks aged 5 weeks aged 7 weeks aged {10 weeks aged

22 Experimental 50 o C (122 o F) is a standard aging temperature used in the industry for shelf life stability testing. Our own test data shows that: one week in 50 o C stability correlates to 6-8 weeks at ambient.

23 Results The cream time did not shift on any formula more than one or two seconds with the exception of formula FR2 The tack free times varied greatly in each of the formulas This was due not only to the type of acid generated in each formula, but also the amount.

24 Formula Name 0 Weeks (Initial) Results 1 Week 3 Weeks 5 Weeks 7 Weeks 10 Weeks Normal Control TEP FR FR FR PS PS PS mfc PE As each formula aged, the acid produced affected each formula differently producing a distinct reactivity aging curve.

25 Each aging curve was compared to others in the same category to determine which ingredients worked best. First, the formulas with different flame retardants will be analyzed. The tack free time data is organized by: Each flame retardant Weeks in stability Data Analysis Formula Name 0 Weeks (Initial) 1 Week 3 Weeks 5 Weeks 7 Weeks 10 Weeks Normal (TCPP) TEP FR FR FR

26 Data Analysis When the data is plotted each formula forms a distinct reactivity curve oC Reactivity Stability Flame Retardant Series Tack Free Time (seconds) TCPP TEP FR1 FR2 FR Weeks in 50oC Stability FR2 performed poorly in the study TEP was the best with TCPP, FR1, and FR3 also performing well

27 Data Analysis The next set to be analyzed is the polyester polyols The tack free time data is organized by each polyester polyol and weeks in stability. Formula Name 0 Weeks (Initial) 1 Week 3 Weeks 5 Weeks 7 Weeks 10 Weeks Normal(PS1) PS PS PS

28 When the data is plotted each formula forms a distinct reactivity curve. 18 Data Analysis 50oC Reactivity Stability Polyester Polyol Series Tack Free Time (seconds) PS1 PS2 PS3 PS Weeks in 50oC Stability In the graphs of the polyester polyols, There is no discernable difference in the aging curves since all formulas drift about the same amount There probably isn t enough polyester polyol in the formula to notice a difference in reactivity between polyols.

29 Data Analysis The next set to be analyzed is the blowing agents The tack free time data is organized by each blowing agent and weeks in stability. Formula Name 0 Weeks (Initial) 1 Week 3 Weeks 5 Weeks 7 Weeks 10 Weeks Normal (ecomate ) mfc

30 Data Analysis When the data is plotted each formula forms a distinct reactivity curve oC Reactivity Stability Blowing Agent Series Tack Free Time (seconds) ecomate 365mfc Weeks in 50oC Stability In this study, the ecomate formula seems to have a little more drift at the beginning, but both formulas follow the same trend and eventually end up at the same reactivity.

31 Data Analysis The next set of formulas examines the 12B56 formula on a more fundamental level This set has Glycerin Polyol 2 put in place of some ingredients in the resin blend. It is assumed that Glycerin Polyol 2 will not contribute to reactivity drift. Formula Name Normal Variation from 12B56 No Change; Same as it is on the previous slide Control Polyester Polyol 1 and TCPP have been replaced with Glycerin Polyol 1 PE2 The TCPP has been replaced with Glycerin Polyol 2

32 Data Analysis The data for this set was organized by formula and weeks in 50 o C stability. Formula Name 0 Weeks (Initial) 1 Week 3 Weeks 5 Weeks 7 Weeks 10 Weeks Normal Control PE

33 25 Data Analysis When the data is plotted, each formula forms a distinct reactivity curve. 50oC Reactivity Stability PE2 Substitution Series 19 Tack Free Time (seconds) 13 6 normal control PE Weeks in 50oC Stability The control was the best with only two seconds of drift Second was PE2 with 4 seconds of drift Then was the Normal formula with 6 seconds of drift This data suggests that the TCPP and polyester polyol both contribute to reactivity drift. It is not known which ingredient contributes more toward drift.

34 Conclusions When assembling a spray polyurethane foam formulas, it is important to choose ingredients that will have the lowest impact on reactivity stability. Proper flame retardant selection is most important since the wrong flame retardant selection can lead to a spray foam with a very short shelf life. Good polyester polyol selection is important to spray foam shelf life, although the study seems to indicate that the choice of polyester polyol does not influence reactivity drift While blowing agent choice will impact shelf life stability, it appears that ecomate has very little effect on spray foam shelf life Fundamentally, flame retardant and polyester polyol have the greatest effect on shelf life

35 Conclusions A polyurethane spray foam optimized for shelf life will have: TEP as its flame retardant A well suited polyester polyol ecomate blowing agent As low as allowable amount of flame retardant and polyester polyol Using these guidelines should lead to a spray foam with a shelf life greater than 8 months.

36 Thank you for your time.